The field of the invention is closed-loop motor control systems, and particularly, systems for controlling the position of movable members on machine tools and the like.
There are numerous position control systems for moving a machine element from one designated point to another. In numerical control systems for example, a series of such moves are stored as digital data which is input to the control system. Such digital data may not only indicate the position to which the movable element is to be driven, but it may also indicate the velocity of the move and the acceleration and deceleration limits of the machine. Feedback devices coupled to the machine provide the position, velocity and acceleration feedback information necessary to maintain the indicated values.
There are numerous instances in which it is desirable to move the machine element as rapidly as possible to a desired position. Such rapid travel is advantageous, for example, when the machine element is being moved into a position from which the actual machining operation can begin. In such rapid moves it is desirable to accelerate and decelerate the movable machine element at the maximum rate possible to minimize the length of time required to make these non-productive moves. Unfortunately, the limit of the machine's capabilities is not known, and in fact, may vary considerably with time, temperature and load. Consequently, the control system is usually "programmed" to accelerate and decelerate the movable element at a reduced, but assured rate.